1. Field of the Invention
The present invention relates to medical catheters and a method of using the same. In one particular aspect the present invention is suitable as a venous return catheter for draining fluid from a vena cava and, or from a right atrium of a heart into extracorporeal life support equipment.
2. Background Information
In many cases requiring heart surgery, the heart and lungs are routinely bypassed with their pumping and gas exchange functions being performed extracorporeally. Venous blood which is low in oxygen content and high in carbon dioxide is mechanically removed from the patient by medical catheters and connecting tubing. The tubing directs the venous blood to a pump and to a gas exchange device which is generally known as an oxygenator. Typically, there is also a heat exchanger incorporated in this circuit. After having carbon dioxide removed and oxygen added in the oxygenator and the temperature modified by the heat exchanger this, now, arterialized blood is returned to the patient by means of connecting tubing and medical catheters.
Medical catheters used to drain the venous blood are generally known as venous return catheters. U.S. Pat. Nos. 4,639,252; 4,129,129; 4,863,441 describe such catheters of single or dual drainage construction. These three patents address the extreme importance of maintaining an adequate flow of blood to supply the patient's needs during extracorporeal life support. Insufficient oxygen or excessive carbon dioxide can produce irreversible tissue damage in the patient while on heart-lung bypass.
U.S. Pat. No. 4,639,252 discusses surgical procedures which require manipulation of the heart which, as discussed, may result in a kinked venous return catheter. In the event that the venous return catheter becomes kinked, the flow to the life support apparatus will be significantly diminished or interrupted. The traditional means to resist kinking have been to make the wall of the catheter sufficiently thick and stiff to reduce the probability of kinking or to imbed coiled wire reinforcement into the wall of the catheter to resist kinking. The wall thickness has a large effect on the flow of a catheter because, according to Poiseuille's Law, flow varies with the fourth power of the inside diameter. Thick-walled catheters have the disadvantage of substantially reducing the flow for a given size catheter-insertion wound. After extracorporeal life support is completed, the catheter-insertion site must be repaired, which also is obviously also affected by the size of the catheter.